Kb261

Emulab FAQ: Troubleshooting: What does the warning message 'due to delay implementation, odd delay value N for LAN may be rounded up' mean?

Emulab FAQ: Troubleshooting: What does the warning message 'due to delay implementation, odd delay value N for LAN may be rounded up' mean?

If you specify a non-zero delay value in make-lan it indicates a one-way delay value for any node to any other on the LAN. One-way LAN delays are implemented by performing half the delay at the sender and half at the receiver. Thus an odd value (e.g., "5ms") would yield a fractional value for each side. Dummynet, which implements delays on shaping nodes, can only handle whole number values and thus the fractional value would be rounded up. The result is that a delay of 5ms would become 6ms in practice and would trigger a warning from linktest.

This does not apply to tb-set-node-lan-delay or tb-set-lan-simplex-params, where the value given indicates the delay from the node to the LAN.